In many rocker arms (in particular, rocker arms with a roller), a pat which pushes a valve stem, and a pivot bearing which bears a pivot, make a connecting portion, and there are provided two side wall portions upright from both ends of the connecting portion. The applicant of the present application has previously disclosed in Japanese Laid-open Patent Publication Number hei 06-159018 (No. JP-A-6-159018) a method of manufacturing a rocker arm, in which a stock is changed in thickness to be subjected to forge processing to make a pat, a pivot bearing, and a pair of sides in a predetermined shape of development, peripheral edges of the sides are subjected to stamping to have a predetermined shape, and thereafter, the sides are subjected to bending to be made upright to form side wall portions. A roller is mounted rotatably on the both side wall portions.
Also, Japanese Laid-open Patent Publication Number hei 10-328778 (No. JP-A-10-328778) discloses a method of manufacturing a rocker arm having a flat, relatively long and narrow shape, in which a multi-stage horizontal, cold forging machine is used to subject a metallic wire rod having a rectangular-shaped section to compression-forming in a diametrical direction by cold forging to form a connecting portion and a side wall portion, which are a little low in dimensional accuracy, and thereafter a connecting portion and a side wall portion, which are high in dimensional accuracy, are formed.
Also, Japanese Laid-open Patent Publication Number 2004-358530 (No. JP-A-2004-358530) discloses a method of manufacturing a rocker arm, in which a multi-stage horizontal, cold forging machine is used to shape a metallic wire rod, having a circular-shaped section, into a drum form, the rod is subjected to compression-forming from both sides in a diametrical direction by cold forging to form a connecting portion and a side wall portion, which are rough in shape and dimension, and thereafter a connecting portion and a side wall portion, which are further close to a finished product in terms of shape and dimension.